In recent years, with miniaturization of electronic instruments and with a trend toward high-frequency operating, semiconductor packages to be mounted therein are required to package devices on a substrate in a high density. With progress of miniaturization and weight-saving, compact packages are being developed which are called micro-BGA (ball grid array) or CSP (chip-size package), external terminals of which are disposed in area array at the lower part of a package.
These packages employ a structure wherein chips are mounted on an organic substrate such as a glass epoxy substrate having a double-layer wiring structure or a polyimide substrate having a single-layer wiring structure, being mounted via an insulating adhesive, where chip-side terminals and wiring-board-side terminals are connected by an inner bonding process such as wire bonding or TAB (tape automated bonding), their connecting areas and chip top surfaces or perimeters are encapsulated with an epoxy type encapsulating material or an epoxy type liquid encapsulating material, and metallic terminals such as solder balls are disposed in area array on the back side surface of the wiring substrate. Then, these packages in plurality are one-time face-bonded on the substrate of an electronic instrument in a high density by solder reflowing. Such a method is being employed.
However, as an example of insulating adhesives used in these packages, an epoxy die-bonding material having a storage elastic modulus at 25.degree. C. of 3,000 MPa or above as measured with a dynamic viscoelastic spectrometer is used, and its connection reliability at solder-ball connected areas (the secondary side) after the packages are mounted on the substrate is so poor as to result in a poor reliability on temperature-cycle resistance.
Moreover, in another example, a liquid silicone elastomer having a storage elastic modulus at 25.degree. C. of 10 MPa or below is proposed as an insulating adhesive. It has a superior temperature-cycle resistance, but has a problem that it has a poor adhesion to the wiring substrate surface at the time of high temperature and a poor moisture-absorbed reflow resistance.
Especially in respect of reflow resistance, in the both examples, voids tend to be included in the course of coating a liquid insulating adhesive on the organic substrate, and faulty modes have been observed such that the voids serve as the starting point from which cracks develop or the organic substrate swells at the time of moisture-absorbed reflowing.
With progress of electronic instruments, electronic component parts are mounted in a higher density, and bare chip packaging on printed-wiring boards is put forward in expectation of a low cost.
As semiconductor chip packaging substrates, ceramic substrates of alumina or the like have been put into wide use. This is chiefly because, since semiconductor chips have a coefficient of thermal expansion of as small as about 4 ppm/.degree. C., it has been required to use a packaging substrate having a relatively small coefficient of thermal expansion so that connection reliability can be ensured, and also it has been required to use a packaging substrate having a relatively high thermal conductivity so that the heat the semiconductor chips generate can be dissipated outside with ease. In the packaging of semiconductor chips on such a ceramic substrate, a liquid adhesive is used which is typified by silver paste.
Filmy adhesives are also used in flexible printed-wiring boards, and systems composed chiefly of acrylonitrile butadiene rubber are in wide use.
In studies on materials relating to printed-wiring boards, those improved in soldering thermal resistance after moisture absorption include an adhesive containing an acrylic resin, an epoxy resin, a polyisocyanate and an inorganic filler as disclosed in Japanese Patent Application Laid-open (KOKAI) No. 60-243180, and an adhesive containing an acrylic resin, an epoxy resin, a compound having a urethane linkage in the molecule and both terminals being primary amine, and an inorganic filler as disclosed in Japanese Patent Application Laid-open (KOKAI) No. 61-138680. These, however, have caused a great deterioration unsatisfactorily when tested on moisture resistance under severe conditions as in PCT (pressure cooker test) treatment.
The use of silver paste adhesives in the packaging of semiconductor chips on the ceramic substrate has had problems that the silver is not dispersed uniformly because of sedimentation of silver fillers, care must be taken for the storage stability of paste, and the operability of semiconductor chip packaging is inferior to LOC (lead-on chip).
The filmy adhesives, though they employ systems composed chiefly of acrylonitrile butadiene rubber are in wide use, have disadvantages that they may cause a great lowering of adhesion after treatment for a long time at a high temperature and have a poor electrolytic corrosion resistance. In particular, they have caused a great deterioration when tested on moisture resistance under severe conditions as in PCT treatment or the like used in an evaluation for reliability of a part associated with semiconductor.
Those disclosed in Japanese Patent Applications Laid-open (KOKAI) No. 60-243180 and No. 61-138680 have caused a great deterioration unsatisfactorily when tested on moisture resistance under severe conditions as in PCT treatment or the like.
These adhesives as materials relating to printed-wiring boards have not been usable because, when semiconductor chips are packaged on a printed-wiring board by the use of any of them, they have so great a difference in coefficient of thermal expansion between the semiconductor chips and the printed-wiring board as to cause cracks at the time of reflowing. They also have not been usable because of a great deterioration occurring when tested on moisture resistance under severe conditions as in temperature-cycle testing, PCT treatment or the like.